Process for recovering aromatic mercaptans from catalytic gasoline



Patented Oct. 10, 1950 PROCESS FOR RECOVERING AROMATIC MERCAPTAN S FROMCATALYTIC GASO- LINE John K. McClennan, Brooklyn, N. Y., and Barney R.Strickland, Westfield, N. J., assignors to Standard Oil DevelopmentCompany, a corporation of Delaware No Drawing. Application September 17,1947,

Serial No. 774,662

4 Claims. (Cl. 260-609) The present invention is concerned with animproved process for the production of aromatic mercaptans. Theinvention is more particularly concerned with the segregation ofaromatic mercaptans or thiophenolic compounds from cracked gasolines,particularly from catalytically cracked gasolines.

It is known in the art-to produce hydrocarbons boiling in the motor fuelboiling range by various distillation, reforming, and crackingprocedures. No attempt will be made to outline or discuss theseprocesses since they are well known. The products from such processesgenerally contain varying amounts of aliphatic and aromatic mercaptans.In general, thermally cracked stocks may contain minor amounts ofaromatic mercaptans, such as thiocresols for example. However,

to a 50% yield of 400 F. end point gasoline, the amount of aromaticmercaptan sulfur in the gasoline is about 0.017 gram per 100 millilitersof gasoline.

As pointed out heretofore, catalytically cracked gasolines containmercaptans, substantially all of which are aromatic in nature. We havenow discovered a peculiar Phenomenon with respect to catalyticallycracked gasolines containing these aromatic mercaptans. We havediscovered that when oxygen is present, oxidation of oleflns anddioleflns in the gasoline is catalyzed by the presence of these aromaticmercaptans. The olefins and dioleflns are oxidized to peroxides, whichin turn destroy the aromatic mercaptans and produce excessive gum in thehydrocarbon mixture.

The aromatic mercaptans which may be present are thiophenols,thiocresols, or thioxylenols.

These may all be considered as being mono. or

di-alkyl substituted thiophenols in which the alkyl group contains oneto three carbon atoms. Specifically, the aromatic mercaptans which maybe present are thiophenol, methyl thiophenol, dimethyl thiophenol, ethylthiophenol, diethyl thiophenol, propyl thiophenol, and dipropylthiophenol.

This phenomenon is fllustrated by the following table:

Table I .Efiect of mercaptans 1 and hydrocarbon composition onperomidation and air sweetening Inspections alter Air InitialInspections Contact Stock Per. Cu Cu Dish ASTM Per. Cu ASTM No. No Gum lGum I No. No. Gum

75 Diisobutylene. {25 Z Dimethyl butadiene} 0 0 4 1 0 0 1 i +n-HeptylMercaptan 0.6 29 6 0.2 0.3 26 3 +Th1ocresol 7.1 27 120 17 13. 7 0 34neptane (base) 0 4 3 0 1 +n-Heiityl Mercaptan; 0 30 5 2 0 33 3 +p-Thocresol.-. trace 28 7 3 trace 26 2 l Mercaptans added to theoreticalcopper number of 30. I Yule, J. A. C. and Wilson, 0. P. Jr. Ind. Eng.Chem. 23, 1254 (1931).

1 Francis, 0. K., Oil 6: Gas Journal 36, No. 11, 99

' Rureau of Mines, Reports of Investigations N0. 3152, November 1931. a

that is, 30 milligrams of mercaptan sulfur per 100 milliliters ofgasoline. This figure corresponds to approximately 0.035% sulfur asaromatic mercaptans. Or again, when a mixed gas oil of about 0.8% sulfuris catalytically cracked noted from the table that the base stockscontained no peroxides and substantially no gum. both before and afterair contact.

Stocks B and C consisted of the base stock A, plus sufiicient mercaptansto result in a theoretical copper number of 30. Similarly stocks E and Fconsisted of the base stock D, plus sufllcient mercaptans to produce atheoretical copper number of 30. Two mercaptans were added to each fuelbase; normal heptyl mercaptan which is an aliphatic mercaptan, andparathiocresol which is an aromatic mercaptan. It will be observed fromthe table that addition of the aliphatic mercaptan to either fuel basedid not appreciably increase the gum content of the blend. The peroxidenumber after contacting with air as contrasted to before contacting withair, was also not increased, indicating that no oxidation took place.

However, in noting the effect of adding the aromatic mercaptan,parathiocresol, to the oleilnic base stock A, it will be observed thatthis was effective in increasing the gum materially after contact withair, and alsoin increasing the peroxide number of the blend after aircontact. This indicates oxidation of the dioleflns and olefins while thedecrease of the copper nun. ber indicates the destruction of thearomatic mercaptan. The resulting gum formation of 34 is excessivelyhigh and would necessitate further acid treating or redistillation. Inthe case where ,parathiocresol was added to normal heptane, it will benoted that the addition of this aromatic mercaptan was not eifective inincreasing the gum content or in changing the peroxide number of thestock.

These results, show that when an aliphatic mercaptan is added to eithera paraflinic or olefinic fuel base, no oxidation of the mercaptan occursand no gum formation results from air contact. on the other hand, whenan aromatic mercaptan is added to an olefinic fuel base, oxidation ofthe mercaptan does occur with resulting gum formation. The fact thatthese results do not occur with paraflinic base fuel stock, shows 7 theimportance of the hydrocarbon composition on these reactions.

These results are further substantiated by the following data securedwith hydrocarbon mixtures boiling in the motor fuel boiling rangederived from catalytically cracked gasolinei The table shows the resultsof tests on two low pressure distillates, mixtures A and B. It will beobserved that after air contact the copper number of these mixtures haddecreased materially while the peroxide number had increased.

These results show the oxidation of oleflns and diolefins in the fuelmixtures with the accompanying destruction of aromatic mercaptans.

The exact mechanism of the reactions involved in this phenomenon is notknown. However, it is believed that olefins and diolefins in thepresence of oxygen, catalyzed by the aromatic mercaptans,

form eroxides which destroy the aromatic mercaptans and form gumproducts. The result is a gasoline containing a relatively large amountof gum which necessitates further treatment of the product.

In accordance with our invention therefore we propose to remove thesearomatic mercaptans, particularly from catalytically cracked gasolines,by treating these gasolines with caustic solution before the crackedstock is allowed to contact oxygen. We then propose to treat and handlethe caustic containing the aromatic mercaptans so as to segregate thearomatic mercaptans.

Aromatic mercaptans may be readily and substantially completely removedby caustic washing, as indicated by the following table.

It will be observed from this table that washing the two samples with10% of a 15 B. sodium hydroxide solution was effective in reducing thecopper number of the samples treated to 2 or less, showing substantialremoval of aromatic mercaptans. Due to the susceptibility of themercaptans to oxidation, it is essential that this process be carriedout in the complete absence of oxygen. If carried out in the absence ofoxygen, the aromatic mercaptans are extracted by the caustic solution ina recoverable form; if oxygen is present, however, the mercaptans areconverted to a form not recoverable with caustic.

The process of our invention may be readily understood by the followingexamples illustrating the same.

Example I Five gallons of a hydrocarbon mixture secured by catalyticallycracking a high sulfur gas oil, of 620 F. mid-boiling point and 1.5%sulfur, at a 968 F. reactor temperature to give a 64% gasoline yield,was treated with 200 milliliters of 20 B. caustic solution in anatmosphere of nitrogen.

' The caustic extract was removed from the oil.

The extract was then acidified and extracted with ether. The ether. wasevaporated and the residual oil stirred with caustic. A portion of theoil was insoluble in caustic and was extracted with ether. This materialhad a 13.55% sulfur content and was probably disulfide formed by airoxidation of mercaptans since some exposure to air had occurred duringhandling. The caustic solution was then acidified to a pH of 11. The oilwhich separated had a sulfur content of 1.97% and a definite cresolodor. The caustic was then acidified to 9 pH. The oil which wasseparated had a sulfur content of 4.38% and a definite cresol odor. Thecaustic was then acidified to a pH of 2 and a third fraction separated.The sulfur content of this fraction was 18.92%. This material had adisagreeableodor resembling that of pure. The following tabulation showsthe fractions obtained:

layers, one layer consisting of the hydroxide solution containing themercaptans, the other layer Table W P ta Mcercizntan ercen ge on entFraction 0! Crude Description urgent by On No.

Product falc. as

T iocresol) Per cent Per cent 10 Material insoluble in caustic 13.55 050 Material liberated at a pH ol approximately 11. 1. 97 0 Materialliberated at pH of approximately 9.-.- 4'. 38 0 20 Material liberated atpH of approximately 2 i8. 92 70 Fraction 4, believed to be thiocresol,was identified as such by preparing the mercury derivative and analyzingit for carbon, hydrogen, sulfur, mercury, and molecular weight. Allvalues obtained checked the theoretical for the mercury derivative ofthiocresol as shown in the following tabulation:

Example II Another operation was run similar to that described withrespect to Example I, except the sample was allowed to be in contactwith air for 16 hours at room temperature. Under these conditions noyield of aromatic mercaptans was secured.

Example III Another experiment was made in which catalytic naphthadistillate was extracted with. aqueous caustic solution, being carefulto exclude all oxygen. The caustic extract was acidified in stages,first to a pH of 9. The oil which separated was extracted with ether andwas essentially phenolic in nature. The caustic extract was then furtheracidified to a pH of 2, whereupon another oily layer separated. Thisproduct was also recovered by extraction with ether and consistedprincipally of thiocresols. The yield of thiocresols obtained in thisexperiment was somewhat greater than was obtained in Example I.

The process of our invention comprises segregating aromatic mercaptans,as for example isomeric thiocresols, from cracked gasolines,particularly from catalytically cracked gasolines. The inventionessentially comprises the initial step of contacting the crackeddistillate boiling in the range from 100 to 400 F. with an alkali metalhydroxide solution capable of dissolving the mercaptans. Sodiumhydroxide, and potassium hydroxide specifically are suitable for thispurpose. It is essential that the gasoline be contacted with thehydroxide solution prior to having the gasoline come in contact withoxygen. The amount and strength of hydroxide solution used is notcritical. The strength may vary from about 5 Be. to about 40 B. and theamount from about 5% to 20%. After contacting with hydroxide solution,the mixture of hydroxide solution and gasoline distillate will separatein two consisting. of the gasoline distillate. The hydroxide layer maybe withdrawn and acidified to segregate the aliphatic mercaptans andphenols from the aromatic mercaptans. While hydrochloric acid was theacid used in the examples to acidify the hydroxide solution, any mineralacid is suitable. The aliphatic mercaptans and phenols are substantiallycompletely released from the hydroxide solution on acidification to a pHof approximately 9. The aliphatic mercaptans and phenols separate as anoily layer which may be withdrawn. The remaining hydroxide solution maythen be acidified to approximately 2 [pH to recover a maximum yield ofaromatic mercaptans. The aromatic mercaptans also separate out as anoily layer which may be withdrawn. During the acidification of thehydroxide solution it is desirable to exclude oxygen, as some olefinsmay still be present in the hydroxide solution. The essence of ourinvention is the segregation of aromatic mercaptans from crackedgasolines in the absence of oxygen by contact with a hydroxide solution,followed by recovery of the aromatic mercaptans by suitableacidification of the hydroxide solution.

Our process may be modified somewhat. For

.example, the hydroxide solution, after removable from the oil, may becompletely acidified rather than acidifying in the step-wise fashion asdescribed. A suitable solvent may then be used to extract aliphaticmercaptans, phenols, and aromatic mercaptans from the hydroxidesolution. For example, ether or a normally liquid light parafiinichydrocarbon, such as pentane or hexane, or a liquid aromatichydrocarbon, such as benzene, may be used as the solvent. The solventmay then be removed to produce a crude residual oil comprising theextracted constituents, that is, aliphatic mercaptans, phenols, andaromatic mercaptans. This crude residual oil may then be treated withcaustic solution which will dissolve the above constituents withoutredissolving the small quantities of entrained oil products stillpresent. The phenols and aliphatic mercaptans may then be separated fromthe aromatic mercaptans as described heretofore by partialacidification.

The process of our invention is not to be limited by any theory as tomode of operation, but only in and by the following claims in which itis desired to claim all novelty insofar as the prior art permits.

We claim:

1. The process for segregating and recovering aromatic mercaptans fromgasolines containing aliphatic mercaptans, phenols, and aromaticmercaptans, which comprises treating'the gasoline in the absence ofoxygen with an aqueous solution of an alkali metal hydroxide selectedfrom the group consisting of sodium hydroxide and potassium hydroxide,withdrawing the hydroxide extract 7 from the gasoline, acidifyingsaid.ext'.act to a pH of about 9 whereby an oily phase separates whichphase comprises the aliphatic mercaptans and phenols, withdrawing saidoily phase, acidifying the remaining hydroxide extract to a pH of about2 whereby a second oily phase separates which phase comprises thearomatic mercaptans, and withdrawing said second oily phase.

2. The process according to claim 1 in which oxygen is excluded from thehydroxide solution.

3. The process according to claim 1 wherein, after acidifying thehydroxide extract respectively to a pH of about 9 and a pH of about 2,the hydroxide solution is extracted with ether.

4. The process of recovering aromatic mercaptans which comprises thesteps of treating a catalytically cracked gasoline in the absence ofoxygen with an aqueous solution of an alkali metal hydroxide selectedfrom the group consisting of sodium hydroxide and potassium hydroxide,withdrawing the hydroxide extract from the gasoline, acidifying saidextract to a pH of about 9 whereby an oily phase separates comprisingthe aliphatic mercaptans and phenols, withdrawing said oily phase,acidifying the remaining hydroxide extract to a pH of about 2 whereby asecond oily phase separates comprising the aromatic mercaptans, andwithdrawing said second oily phase.

JOHN K. MCCLENNAN.

BARN'EY R. STRICKLAND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,704,246 Halloran Mar. 5, 19291,752,709 Stoll Apr. 1, 1930 2,013,203 Davis et a1 Sept. 3, 19352,053,752 Vobach et a1 Sept. 8, 1936 2,218,139 Benson et al. Oct. 15,1940 2,222,170 Craig et a1 Nov. 19, 1940 2,245,317 Bannerot June 10,1941 2,364,416 Ayers et al Dec. 5, 1944

1. THE PROCESS FOR SEGREGATING AND RECOVERING AROMATIC MERCAPTANS FROMGASOLINES CONTAINING ALIPHATIC MERCAPTANS, PHENOIS, AND AROMATICMERCAPTANS, WHICH COMPRISES TREATING THE GASOLINE IN THE ABSENCE OFOXYGEN WITH AN AQUEOUS SOLUTION OF AN ALKALI METAL HYDROXIDE SELECTEDFROM THE GROUP CONSISTING OF SODIUM HYDROXIDE AND POTASSIUM HYDROXIDE,WITHDRAWING THE HYDROXIDE EXTRACT FROM THE GASOLINE, ACIDIFYING SAIDEXTRACT TO A PH OF ABOUT 9 WHEREBY AN OILY PHASE SEPARATES WHICH PHASECOMPRISES THE ALIPHATIC MERCAPTANS AND PHENOIS, WITHDRAWING SAID OILYPHASE, ACIDIFYING THE REMAINING HYDROXIDE EXTRACT TO A PH OF ABOUT 2WHEREBY A SECOND OILY PHASE SEPARATES WHICH PHASE COMPRISES THE AROMATICMERCAPTANS, AND WITHDRAWING SAID SECOND OILY PHASE.